The effects of river flow on water quality in estuarine impoundments

Several impoundment schemes have been built or are proposed in the UK and w orldwide. Impounding fundamentally alters the dynamics of estuaries with co nsequences in terms of sedimentation patterns and rates as well as water qu ality. This paper presents some initial findings on the relationships of wa ter quality to river flow based on work done on the Tees impoundment in Nor theast England (a total exclusion system) in the summer of 1999 and the win ter of 2000. Eleven water quality surveys were undertaken to measure a rang e of water quality parameters (BOD, alkalinity, pH, Eh, conductivity, disso lved oxygen, temperature, suspended solids, nitrate plus nitrite, ammonium and orthophosphate, and a range of metals) over a variety of states of rive r flow. Statistical analysis was used to determine whether the major water quality parameters were controlled by processes internal to the impoundment , i.e. with water depth and distance downstream, or external inputs to the impoundment. Those reported as controlled by external inputs include nitrat e and nitrite, phosphate, dissolved oxygen, dissolved metals, conductivity, alkalinity, and temperature. pH, and to a minor extent dissolved oxygen an d nutrients, show internal control. Understanding the controls on water qua lity parameters will allow more sustainable management of such schemes. (C) 2001 Elsevier Science Ltd. All rights reserved.